1. Field of the Invention
The present invention relates to a method for forming a color image with excellent coloring property (or color development) and color uniformity. Particularly, the present invention relates to a liquid composition and an ink set comprising the liquid composition suitable for image formation by an ink-jet recording system, a method for forming a colored portion on a recording medium; and an ink-jet recording apparatus employing the ink set.
2. Related Background Art
The ink-jet recording system conducts recording by ejecting an ink onto a recording medium like a paper sheet. For example, ink-jet recording systems which employ an electro-thermal transducer are disclosed in Japanese Patent Publication Nos. 61-59911, 61-59912, and 61-59914 as an ejection energy supplying means and eject liquid droplets by bubbles formed in the ink by thermal energy. In such an ink-jet recording system, the recording head orifice can readily be multiplied in a high density to obtain images with high resolution and high quality at a high speed.
In conventional ink-jet recording systems, the ink is mainly composed of water and contains a water-soluble high-boiling solvent such as glycol to prevent drying of ink in the nozzle and clogging of the nozzle, and for other purposes. Such an ink may cause problems of incomplete fixation of the ink, or nonuniformity of the formed image presumably caused by nonuniform distribution of a filler or a sizing agent on the face of a recording medium paper sheet. On the other hand, in recent years, the ink-jet record is required to have a high image quality comparable to that of a silver salt photograph, and to give a higher image density and a broader color reproduction range of the ink-jet recorded image, and higher uniformity of the color of the record.
In such circumstances, many methods are disclosed for stabilization of the ink-jet recording process and improvement of quality of ink-jet recorded images. One disclosed method is coating of the surface of the base paper sheet or a recording medium with a filler or a sizing agent. For example, porous fine particles capable of adsorbing a coloring material are applied as a filler on a base paper sheet to form an ink-receiving layer. Coat paper sheets for ink-jet recording are commercially produced by employing such techniques.
In such circumstances, may methods are disclosed for stabilization of the ink-jet recording and improvement of quality of ink-jet recorded matters. Other typical methods are summarized below.
(1) Incorporation of a Volatile Solvent, or a Penetrative Solvent into an Ink:
Japanese Patent Application Laid-Open No. 55-65269 discloses addition of a compound which promotes penetration of a surfactant or the like into the ink for accelerating fixation of the ink on the recording medium. Japanese Patent Application Laid-Open No. 55-66976 discloses an ink mainly composed of a volatile solvent.
(2) Mixing of an Ink with a Liquid Composition Reactive to the Ink on a Recording Medium:
An image-improving liquid composition is applied on a recording medium, before or after application of a recording ink, to improve image density and water resistance and to prevent bleeding.
Japanese Patent Application Laid-Open No. 63-60783 discloses preliminary application of a basic polymer-containing liquid composition and subsequent recording with an anionic dye-containing ink. Japanese Patent Application Laid-Open No. 63-22681 discloses a recording method in which a first liquid composition containing a reactive chemical species and a second liquid composition containing a compound capable of reacting with the reactive chemical species are mixed on a recording medium. Japanese Patent Application Laid-Open No. 63-299971 discloses preliminary application of a liquid composition containing an organic compound having two or more cationic groups in the molecule onto a recording medium and subsequent recording with an ink containing an anionic dye. Japanese Patent Application Laid-Open No. 64-9279 discloses a recording method in which an acidic composition containing succinic acid or the like is applied onto a recording medium and subsequently recording is conducted with an ink containing an anionic dye.
Japanese Patent Application Laid-Open No. 64-63185 discloses application of a liquid composition capable of insolubilizing an ink dye before recording with an ink. Japanese Patent Application Laid-Open No. 8-224955 discloses use of a liquid composition containing cationic substances of different molecular distribution ranges in combination with an ink. Japanese Patent Application Laid-Open No. 8-72393 discloses use of a liquid composition containing a cationic substance and finely pulverized cellulose in combination with an ink. These methods gives excellent image with high image density, high print quality, high water resistance, high color reproducibility, and less bleeding. Japanese Patent Application Laid-Open No. 55-150396 discloses application of a water resistance-imparting agent which forms a lake by reaction with the dye after recording with a dye ink to improve water resistance of a recorded image.
(3) Mixing of an Ink with a Fine Particle-containing Liquid Composition on a Recording Medium:
Japanese Patent Application Laid-Open No. 4-259590 discloses application of colorless liquid containing colorless inorganic fine particles on a recording medium and subsequent application of nonaqueous recording liquid thereto. Japanese Patent Application Laid-Open No. 6-92010 discloses a method in which a solution containing fine particles or a solution containing fine particles and a binder polymer is applied first and subsequently an ink containing a pigment, a water-soluble resin, a water-soluble solvent, and water is applied. These methods are said to give images with high print quality and high coloring property.
(Background Technique)
The inventors of the present invention, after comprehensive investigation on various ink-jet recording techniques as mentioned above, found that the above described methods achieve remarkable effects in solving the respective technical problems, but other ink-jet recording properties may be impaired instead. For example, the aforementioned recording medium having a surface of a base paper sheet coated with a filler or a sizing agent (hereinafter referred to as xe2x80x9ca coat paper sheetxe2x80x9d) is recognized to be capable of forming a high-quality image.
Generally, for obtaining an image of high chroma, it is known that the coloring material should be retained on the surface of a recording medium in a monomolecular state without aggregation. The fine porous particles on the coat paper sheet serve surely to retain the coloring material. However, for achieving a high image density and high image chroma, a larger amount of the porous fine particles is required to form a thick ink-receiving layer to cover the base paper sheet, which impairs the feel of the base paper sheet. The inventors of the present invention presumed that such a thick ink-receiving layer is required because the coloring material is not effectively adsorbed by the porous fine particles.
For the explanation below, a coat paper sheet is taken which has one ink-receiving layer. FIG. 9 shows schematically a cross section of a surface and its vicinity of the coat paper sheet. In FIG. 9, the numeral 901 denotes a base paper sheet, the numeral 903 denotes an ink-receiving layer, and the numeral 909 denotes a coloring material. The ink receiving layer 903 contains porous fine particles 905 and an adhesive 907 for fixing the porous fine particles. The ink applied on the paper sheet penetrates into interstices between the porous fine particles by capillarity to form ink penetration regions. Since the porous fine particles distribute not completely uniformly as shown in FIG. 9, the penetration is not uniform locally, and the penetration of the ink by capillarity is also not uniform locally. Therefore, in the process of penetration of the ink, the coloring material 909 is not brought into uniform contact with the surface of the porous fine particles, resulting in ineffective adsorption of the coloring material by the porous fine particles.
Moreover, the adhesive 907 may hinder the penetration of the ink in some portions to leave non-penetrated regions which do not contribute the coloring property. From the above reasons, in a conventional coat paper sheet, the porous fine particles cannot effectively adsorb the coloring material in a monomolecular state for the amount of the particles. Therefore, a larger amount of the porous fine particles should be used for obtaining a high-quality image, which impairs the feel of the base paper sheet.
By employing the above technique (1), fixation of an ink on a recording medium is improved, but the image density and the color reproduction range, which is important in recording on plain paper or in color image recording, may become insufficient. Further, according to the above technique (2), high image density owing to retention of coloring material in the ink on the surface of a recording medium is achieved, but the color reproduction range or chroma may be lowered, probably owing to agglomeration of the coloring material on the surface of the recording medium. Thus, since the conventional methods have problems, in order to obtain a higher quality ink-jet recording image that has been sought recently, the inventors have recognized the need for the development of novel ink-jet recording techniques. The present invention is based on such new recognitions.
Accordingly, an object of the present invention is to provide a liquid composition to be used for obtaining ink-jet recording images having higher quality.
An object of the present invention is also to provide a method for forming colored area onto a recording medium in which superior ink-jet recording matter having broad color reproduction area, superior color uniformity, less stripy unevenness at solid parts and good rub-off resistance can be formed on a plain paper.
Another object of the present invention is to provide a liquid composition which can form an ink-jet recording image having a broad color reproduction area, superior color uniformity, less stripy unevenness at solid parts and good rub-off resistance, an ink set in a combination with the liquid composition and an ink-jet recording apparatus.
In an embodiment of the present invention, the present invention is to provide an aqueous liquid composition for forming a colored area of an image on a recording medium by application with an anionic or cationic aqueous ink containing a coloring material, the aqueous liquid composition containing fine particles dispersed therein and the fine particles being charged at a surface in a polarity opposite to the ink.
In another embodiment of the present invention, the present invention is to provide an ink set comprising an aqueous anionic or cationic ink containing a coloring material and an aqueous liquid composition containing fine particles dispersed therein and being charged at a surface in a polarity opposite to the ink in a combination.
In still another embodiment of the present invention, the present invention is to provide a method for forming a colored area of an image comprising the steps of: (i) applying an aqueous anionic or cationic ink containing a coloring material onto a recording medium; and (ii) applying onto a recording medium a liquid composition containing fine particles dispersed therein and electrically charged at a surface in a polarity opposite to the ink, wherein the aqueous ink and the liquid composition are brought into contact in a liquid-liquid state.
In still another embodiment of the present invention, the present invention is to provide an ink-jet recording apparatus comprising a first recording unit having an ink container for holding an aqueous anionic or cationic ink containing a coloring material, and a first ink-jet head for ejecting the ink; and a second recording unit having a liquid composition container for holding a liquid composition containing fine particles dispersed therein and electrically charged at the surface in a polarity opposite to the aqueous ink, and a second ink-jet head for ejecting the liquid composition.
In still another embodiment of the present invention, the present invention is to provide a liquid composition for forming a colored area of an image on a recording medium with a cationic or anionic ink containing a coloring material, the coloring material being in a molecular state in the ink, the liquid composition comprising a fine particle, wherein the particle adsorbs or binds the coloring material on the surface thereof with substantially maintaining the molecular state to form the colored area when the ink and the liquid composition are brought into contact with each other in a liquid-liquid state.